1. Field of the Invention
The present invention relates generally to reducing cooling air leakage between adjacent flowpath segments in gas turbine engines, such as leakage between adjacent turbine nozzle segments. More particularly, the invention relates to a flexible three-piece seal assembly which can include first and second spline seals in abutting engagement with a third seal member.
2. Description of Known Art
Gas turbine engines typically include nozzle diaphragms and shroud assemblies centered about the engine's axis and forming annular flowpath boundaries within the engine. Due to the large temperature differentials encountered during engine operation, these nozzles and shrouds are typically designed as an assembly of circumferentially spaced-apart segments with gaps extending between adjacent segments. The gaps accommodate differential thermal growth and reduce thermal stress in the flowpath segments.
These flowpath segments are generally exposed to high temperature gas flows and are typically cooled with high pressure cooling air bled from an upstream compressor. Such cooling air bled from the compressor is parasitic and must be minimized to the extent possible to maximize engine efficiency. As a result, it is highly desirable to reduce cooling air leakage through the circumferentially extending gaps between nozzle segments and other flowpath segments.
Various seal designs are known for providing sealing between flowpath segments in gas turbine engines, such as those designs shown in U.S. Pat. Nos. to Bertelson (3,728,041), Grosjean (4,537,024), Bowers et al. (3,752,598), and Clevenger et al (4,767,260).
Sealing arrangements using spline or feather seals are commonly used in gas turbine engines. Such seals are typically disposed in pairs of oppositely facing grooves electro-discharge machined in oppositely facing surfaces on adjacent flowpath segments. Such seals are flexible and include some freedom of movement in their respective grooves to accommodate manufacturing tolerances, surface roughness in the grooves, and misalignment or movement between adjacent flowpath segments. Seals which are not flexible will not seat properly in the grooves, resulting in leakage and wasted cooling flow.
In addition, two such seals may be used in combination to seal leakage flow in both a generally radial and a generally axial direction between adjacent flowpath segments. Prior seal assemblies have been ineffective, however, since they typically include a leakage path between the two seals, or introduce stiffness to the seal assembly, or couple the motion of one seal with the motion of another seal.